One example of known techniques for efficiently guiding light incident on a window glass into the indoor is disclosed in Patent Literature (PTL) 1. According to the technique disclosed in PTL 1, a daylighting film includes a plurality of unit prisms, which have the daylighting function and which are formed on one surface of an optically-transparent support, and the daylighting film is pasted to an outer surface (outdoor side surface) of the window glass with the unit prisms facing the outside. Light incident on the daylighting film from the unit prism side is refracted at surfaces of the unit prisms and enters the indoor after passing through the unit prisms, the support, and the window glass.
In the case of pasting the daylighting film to the window glass, if structural elements (projections) with the daylighting function are exposed to the outside, there is a possibility that the structural elements (projections) may be contaminated or deformed with impacts. Therefore, the structural elements (projections) need to be covered with a separate base member. PTL 2 and PTL 3 disclose structures including protective base members to prevent damage of the daylighting film.